Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!att!pacbell.com!ucsd!ogicse!emory!athena.cs.uga.edu!mcovingt
From: mcovingt@athena.cs.uga.edu (Michael A. Covington)
Newsgroups: sci.electronics
Subject: Re: 12V car --> 3V cd player
Keywords: CD, cd, cd player, car, power supply
Message-ID: <1991Jan1.002202.19182@athena.cs.uga.edu>
Date: 1 Jan 91 00:22:02 GMT
References: <1990Dec31.081024.16910@yenta.alb.nm.us> <2374@casbah.acns.nwu.edu> <%BS^BG*@rpi.edu>
Organization: University of Georgia, Athens
Lines: 24

In article <%BS^BG*@rpi.edu> wrf@mab.ecse.rpi.edu (Wm Randolph Franklin) writes:
>In article <2374@casbah.acns.nwu.edu> squishy@casbah.acns.nwu.edu (Shishin Yamada) writes:
>>
>>+12V   Fuse    L1              1 _________ 2        D1   D2   D3
>>O-------O~O---UUUUU---+------+---|       |-----+---->|--->|--->|----O  +3V
>>                     +|      |   | 7805  |     | 
>>                     ===    ===  |_______|    === C3
>>Ground                | C1   | C2    |3        |
>>O---------------------+------+-------+---------+--------------------O Ground
>>
>>	Where, L1 is say 1 uH, C1 is say 2200uF, C2 is 0.33uF, C3 is 0.1uF,
>>D1 D2 and D3 are silicon rectifying diodes (like 1N4001). All components
>>should be rated at least to 16 volts.
>
>What does C2 do since it's so much smaller than C1?  My guess it that it
>also has a smaller  inductance and  so traps hi  freqs better.   Is this
>right?  Thanks.
>

Series resistance. A big electrolytic capacitor, especially if not
tantalum, will have a couple of ohms of series resistance, and to that
extent will not be a good filter for high frequencies. That's why a
capacitor of the conventional type (polyester, or whatever), much lower
capacitance, is put in parallel with it.